Microbial interactions impact stress tolerance in a model oral community

Microbial interactions are critical modulators of the emergence of microbial communities and their functions. However, how these interactions impact the fitness of microbes in established communities upon exposure to environmental stresses is poorly understood. Here, we utilized a two-species community consisting of <i>Aggregatibacter actinomycetemcomitans</i> and <i>Streptococcus gordonii</i> to examine the impact of synergistic and antagonistic interactions on microbial resilience to environmental fluctuations and susceptibility to microbial invasion. We focused on the <i>S. gordonii</i>-produced extracellular molecules, L-lactate and H₂O₂, which have been shown to mediate interactions between these two microbes. We discovered that seemingly beneficial functions, such as <i>A. actinomycetemcomitans</i> cross-feeding on <i>S. gordonii</i>-produced L-Lactate, can paradoxically exacerbate vulnerabilities, such as susceptibility to antibiotics. Moreover, our data highlight the context-dependent nature of microbial interactions, emphasizing that a seemingly potent antimicrobial, such as H₂O₂, can have both synergistic and antagonistic effects on a microbial community dependent on the environment.